A compound bow has been being improved for almost 40 years since its invention in 1969 as the size of it has become compact-sized whereas forgiveness is being enhanced, and the speed of an arrow becomes faster.
The above-mentioned improvements thank to the use of new materials and new designs of cam.
The cams of a compound bow play an important role in terms of let-off and energy storage.
In the original compound bow, only one eccentric cam was used at an end portion of a limb of one side; however as the compound bow is improved, the construction of the cam is complicated. In recent years, a differential motion cam is generally used, in which two cams are engaged at an end portion of a limb.
In the original compound bow, since a distance between the axles (A to A; Axle to Axle) was long, so a relatively smaller cam and a relatively weaker limb and a riser could be used; however as the compound bow becomes compact-sized, the size of a cam has increased, and a stronger limb and a riser are needed. So, the weight of a compound bow has increased even though new materials are adapted.
The riser represents a part including a grip, and not includes limbs and a string. In the present invention, a riser outwardly extended from where a conventional limb was attached is used, and a riser propria (RP) means an inner side of a portion where a conventional limb was attached to a riser, and a riser extended (RE) means an outer side of a portion where a conventional limb was attached to. In addition, there is a riser supportive (RS) which is an element supporting a riser extended and a riser propria for the purpose of reducing the weight of a riser by distributing the force applied to the riser extended and the riser propria.
The outer circumference means a circumference of a circle as well as an ellipse and a groove of a cam, all of which hereinafter are used as the same meaning.
In case of a compound bow which has a small amount of limb movement, the length of a string to be released, which is wound on a groove of a cam and the distance between the axles are subject to determining a draw length in a large part. So, the string to be released, which is wound on the groove of the cam, is defined as a string releasable (SR).
The differential motion pulley means a pulley assembly formed of pulleys with different diameters and is generally used for the purpose of a speed change or a tensile force change. In the present invention, pulleys as well as cams are used. It is defined as a differential motion cam and includes a differential motion pulley. In the differential motion cam, a smaller cam is defined as a small lobe and a larger cam is defined as a large lobe.
The Y-shaped buss cable is generally used as a buss cable of a compound bow. In the present invention, a Y-shaped buss cable and a Y-shaped string are used, and a cam with a groove for fitting them is newly invented and adapted in the present invention, which is defined as a Y-cam. In case of a circular shape, it is defined as a Y-pulley; however it belongs to a Y-cam. One stem before it is branched from a Y-shape is defined as a Y-body, and two branches after it is branched are defined as a Y-limb.
The related technologies are as follows.
The U.S. Pat. No. 7,143,757 B1 Cooper Dec. 5, 2006 discloses a technology which is characterized in that a rotational amount of a cam module is possible up to 270° without a string being overlapped.
The U.S. Pat. No. 7,047,958 B1 David E. Colley May 23, 2006 discloses a technology which is characterized in that only an idler pulley is positioned at an end portion of a flexible limb, and a cam is positioned at a non-flexible riser, and a pulley adapted for a synchronization of upper and lower pulleys is positioned at a plane different from a flying direction of an arrow, thus making it possible to eliminate the member of a cable guard.
The WO 2008/108766 AI PCT/US2007/005834 SIMS, Steven, 1 Mar. 2007 discloses a technology which is characterized in that no pulley or cam is provided at an end portion of a flexible limb, and a differential motion cam is positioned at a non-flexible riser.
The Korean application number 10-2010-0023200 Park, Kyung-shin and Korean application number 10-2010-0036300 Park, Kyung-shin disclose the technologies which are directed to resolving the problems that the string is overlapped; however there are a lot of problems in the shaft of the cam.